Introduction to DSA

🔹 Dependency Injection

**Dependency Injection (DI)** is a design pattern used to achieve **Inversion of Control (IoC)** in object-oriented programming. It allows a class to receive its dependencies from an external source rather than creating them internally.

📌 Why Use Dependency Injection?

Dependency Injection helps in **loosely coupling** components, making code more modular, testable, and maintainable.

✅ **Improves Code Maintainability** – Reduces hard dependencies between classes.
✅ **Enhances Testability** – Makes it easier to write unit tests using mock dependencies.
✅ **Promotes Reusability** – Decouples implementation details from class behavior.

💡 Real-Life Example

Consider a **Car** that needs an **Engine**. Instead of the Car creating an Engine internally, we inject an Engine dependency from outside.

🖥️ Dependency Injection in Java (Spring Framework)

Spring's **@Autowired** annotation injects dependencies automatically.


            import org.springframework.beans.factory.annotation.Autowired;
            import org.springframework.stereotype.Component;
            
            @Component
            class Engine {
                public void start() {
                    System.out.println("Engine started...");
                }
            }
            
            @Component
            class Car {
                private final Engine engine;
            
                @Autowired
                public Car(Engine engine) {
                    this.engine = engine;
                }
            
                public void drive() {
                    engine.start();
                    System.out.println("Car is driving...");
                }
            }

🖥️ Dependency Injection in Python

In Python, DI can be implemented using constructor injection.


            class Engine:
                def start(self):
                    print("Engine started...")
            
            class Car:
                def __init__(self, engine):
                    self.engine = engine
                
                def drive(self):
                    self.engine.start()
                    print("Car is driving...")
            
            engine = Engine()
            car = Car(engine)
            car.drive()

🎯 Summary